How bad is SLOC (source lines of code) as a metric? [closed]

问题

We are documenting our software development process. For technical people, this is pretty easy: iterative development with internal milestones every four weeks, external every 3 months.

However, the purpose of this exercise is to expose things for our project management in terms that they can understand. Specifically, these non-technical managers need metrics that they can understand.

I understand our options for metrics well and have proposed a whole set (requirements met and actual costs vs. budgeted costs are two of my favorites). However, we do have some old hands involved and they tend to hang onto metrics like SLOC.

I understand the temptation of SLOC: it seems easy for non-software people to understand and it seems like the closest analog of a physical thing (it's just like counting punched cards back in the old days!).

So here's the question: how can I explain the dangers of SLOC to a non-technical person?

Here's some concrete motivation: we work on a fairly mature deployed system that has years of history behind it. As we add features, SLOC tends to stay approximately level or even decrease (refactoring removes old / dead code, new features are really just adjustments of existing, etc). To a non-programmer manager, a non-increasing SLOC in a development project is perplexing at best....

Clarifying in response to a recent answer below: remember, I'm arguing that SLOC is a bad metric for the purposes of measuring project progress. I'm not arguing that it is a number that's not worth collecting. It requires extensive context to do anything useful with it and most program managers don't have that context.

回答1:

Someone said :

"Using SLOC to measure software progress is like using kg for measuring progress on aircraft manufacturing"

It is totally inappropriate as it encourages bad practices like :

Copy-Paste-Syndrome
discourage refactoring to make things easier
Stuffing with meaningless comments
...

The only use is that it can help you to estimate how much paper to put in the printer when you do a printout of the complete source tree.

回答2:

The issue with SLOC is that it's an easy metric to game. Being productive does not equate to producing more code. So the way I've explained it to people baring what Skilldrick said is this:

The more lines of code there are the more complicated something gets.
The more complicated something gets, the harder it is to understand it.
Before I add a new feature or fix a bug I need to understand it.
Understanding takes time.
Time costs money.

Smaller code -> easier to understand -> cheaper to add new features

Bean counters can understand that.

回答3:

回答4:

Show them the difference between:

for(int i = 0; i < 10; i++) {
    print i;
}

and

print 0;
print 1;
print 2;
...
print 9

And ask them whether 10 SLOC or 3 SLOC is better.

In response to the comments:

It doesn't take long to explain how a for loop works.
After you show them this, say "we now need to print numbers up to 100 - here's how you make that change." and show how much longer it takes to change the non-DRY code.

回答5:

I disagree on SLOC being a bad metric. It may be moot to go into a years-old question with eleven answers, but I'll still add another.

Most arguments call it a bad metric because it is not suited to directly measure productivity. That is a strange argument; it assumes the metric to be used in an insane way. With this reasoning, one could call the Kelvin a bad unit because it is unsuited to measure distance.

Code length is a viable measure of ballast.

The amount of non-comment code lines correlates with:

undetected errors
maintenance costs
training time for new contributors
migration costs
new feature costs

and many more similar kinds of costs, like the cost of optimization.

Of course SLOC count isn't a precise measure of any of these. Code can be anywhere between very nice and very ugly to manage. But it can be assumed that code length is rarely free, and thus, longer code is often harder to manage.

If I were managing a team of programmers, I would very much want to keep track of the ballast it creates or removes.

回答6:

Explain that SLOC is an excellent measurement of the lines of code in the application, nothing else.

The number of lines in a book, or the length of a film doesn't determine how good it is. You can improve a film and shorten it, you can improve an application and reduce the lines of code.

回答7:

Pretty bad (-:

A much better idea would to cover the test cases, rather than code.

The idea is this: a developer should commit a test case that fails, then commit the fix in next build, and the test case should pass ... just measure how many test cases the developer added.

As a bonus collect coverage stats (branch coverage is better than line coverage here).

回答8:

You don't judge how good(how many features,how it performs..) a plane is based on its weight(sloc).

When you want your plane to fly higher, longer and perform better, you don't add weight to it. You replace parts of it with lighter/better materials. You strip off parts you don't need as to not add unnecessary weight.

回答9:

I believe SLOC is a great metric. It tells you how large your system is. That is good for judging complexity and resources. And it helps you prepare the next developer for working on a codebase.

But SLOC count should be analyzed only AFTER other appropriate code quality metrics have been applied. So...

Do NOT write 2 lines of code when 1 will do, unless the 2-line version makes the code 2 times easier to maintain.
Do NOT fluff code with unnecessary comments just to fluff SLOC count.
Do NOT pay people by SLOC count.

I have been managing software projects for 30 years. I use SLOC count all the time, to help understand mature systems. I have never found it useful to even glance at SLOC count until a project is near version 1.0 release.

Basically, during the development process, I worry about quality, performance, usability, and conformance to specifications. Get those right, and the project will probably be a success. When the dust settles, look at SLOC count. You might be surprised that you got SO much out of 5,000 lines of code. And you might be surprised that you got SO little! (But SLOC count does not affect quality, performance, usability, and conformance to specification.)

And always code like the person who will be working on your code next is a violent psychopath who knows where you live.

Cheers, Uncle Chip

回答10:

even modern code metrics tools criticize SLOC conting, i like the point made in the ProjectCodeMeter FAQ:

What's wrong with counting Lines Of Code (SLOC / LLOC)?

回答11:

Why SLOC is bad as an individual metric of productivity

Think of code as a block of clay/stone. You need to carve, say 10 statues. It's not how many statues you carve that counts. It's how well you've carved it that counts. Similarly it's not how many lines you've written but how well they are functioning. In case of code LOC can backfire as a metric this way.

Productivity also changes when writing a complex piece of code. It takes a second to write a print statement but a lot of time to write a complex piece of logic. Not all fingers are equal.

How SLOC can be used to your benefit

I think SLOC for defect % is a good metric. Yes the difficulty level comes into play but this is a good parameter that the managers can throw around while doing business. Try to think from their perspective too. They don't hate you or your work, but they need to tell customers that you're the best and for that they need something tangible. Give them what you can :)

回答12:

SLOC can be changed dramatically by putting extra empty lines ("for readability") or by putting or removal of comments. So relying on SLOC only can lead to confusion.

回答13:

Why don't they understand that the SLOC hasn't changed, but the software does more than it did yesterday because you've added new features, or fix bugs?

Now explain it to them like this. Measuring how much work was done in your code by comparing the lines of code is the same as measuring how many features are in your cell phone comparing it by size. Cell phones have decreased in size over 20 years time while adding more features because of technological improvements and techniques. Good code follows this same principal as we can express the same logic in fewer and fewer lines of code, making it faster to run, easier to maintain, and simpler to understand as we improve our understanding of the problem and introduce new techniques for development.

I would get them to focus on the business value returned through feature development, maintenance, and bug fixes. If whoever is happy with the software says they can see improvement don't sweat the SLOC.

Go read this:

https://stackoverflow.com/questions/3800707/what-is-negative-code

来源：https://stackoverflow.com/questions/3769716/how-bad-is-sloc-source-lines-of-code-as-a-metric

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